Automated conveyor systems are often used to assemble intricate or delicate workpieces. Pallet-type carriers which ride on top of the conveyors are used to transport the workpieces from one work station to another in the system. A pallet-type carrier usually consists of a flat pallet used to carry a workpiece and a lower shoe or puck that rides on top of the moving conveyor. The shoe may also be referred to as a pallet guide.
Pallet-type carriers will often transport a workpiece from one station to another in a condition where the workpiece is not completely assembled or in a very fragile state. It is imperative to keep the workpiece and the pallet, on which the workpiece rests, in a horizontal position when transporting the workpiece from one station to another station because loose parts that are not securely attached to the workpiece may fall off of the pallet between work stations. Further, loose parts may fall off the pallet or become dislodged when the carrier makes a sharp turn, such as a 90.degree. turn. Any tilt of the pallet, in combination with the natural centrifugal forces exerted on the workpiece during a sharp turn, can damage the workpiece or cause loose parts to be dislodged during the turn.
Further, in addition to maintaining the pallet in a horizontal position, providing a smooth ride for the workpiece is essential. Accordingly, the pallet-type carrier should preferably be equipped with shock-absorbing and vibration-dampening means. Currently, pallet-type carriers are not adequately equipped and delicate workpieces or parts from workpieces are often lost as the pallet-type carrier is transported from station to station along the conveyor line. Specifically, the portion of the pallet-type carrier that engages the conveyor is known as a pallet-guide, shoe or puck. While it is known to attach the shoe to the pallet portion of the carrier with a spring-biased mechanism, none of the mechanisms known are adjustable. Accordingly, the shock absorption and vibration dampening characteristics of the spring-biased mechanisms are minimal because they cannot be adjusted for changing conditions, such as changing conveyor speeds. Accordingly, an adjustable shock absorption and vibration dampening system for the shoes or pucks is needed.
Therefore, there is a need for pallet-type carriers for use on automatic conveyor systems that are stabilized in the horizontal plane and further that include shock-absorbing and vibration-dampening means. The stabilized pallet-type carriers must be able to transport workpieces from one station to another in a smooth fashion and maintain the general flat or horizontal position of the pallet while the carrier is being transported on the conveyor. Further, the stabilized pallet-type carrier must be able to make sharp turns while maintaining the general flat or horizontal position of the pallet. Finally, as much vibrational energy as possible should be absorbed before it reaches the workpiece.
Another feature of the pallet-type carrier that can affect the performance of the entire system is the shoe or pallet guide. The shoes are currently provided in two forms. First, a polyurethane shoe is popular with manufacturers because it is lightweight, requires less energy to transport on top of the conveyor and, because of its lightweight, polyurethane can reduce the amount of friction between the undersurface of the shoe and the top of the conveyor.
However, polyurethane shoes have not proven entirely satisfactory over time. Specifically, the polyurethane shoes tend to wear prematurely. When used in environments where dust, dirt and grime are present, dirt particles become embedded in the polyurethane shoe. When the polyurethane shoe, embedded with dirt particles, passes over the conveyor, the resulting action is much like rubbing sandpaper on top of the conveyor. As a result, the conveyor chains wear prematurely.
A second type of shoe is one fabricated entirely out of metal. Metal shoes last longer than polyurethane shoes. Further, dust, dirt or grime particles do not become embedded in the undersurface of the metal shoes and therefore the undersurface of the metal shoes remains smooth and does not cause premature wear to the conveyor chain.
However, the metal shoes are much heavier than the polyurethane shoes and when a plurality of pallet-type carriers are employed on a single conveyor, the overall weight transported by the carrier is increased dramatically. Therefore, there is a need for an improved shoe or pallet guide for pallet-type carriers that combines the lightweight of polyurethane or other polymeric materials with the superior wear characteristics of metal shoes, including steel shoes.